PURPOSE: To realize accurate and stabilized torque control and engaging/ disengaging of clutch on the output side by displacing a shutter, made of ferromagnetic material, in the gap between magnetized parts of each rotary body.

CONSTITUTION: When a shutter 10 is displaced gradually, an opening 14 shifts from rotary bodies 4, 8 and the magnetic force of lines, existing between magnetized parts 3, 7, is blocked gradually by means of the ferromagnetic shutter 10 and thereby the torque of a rotary shaft 5 decreases correspondingly and the rotary shaft 5 stops when the torque decreases below a load torque. Since the torque of the rotary shaft 5 on the output side can be regulated smoothly and continuously according to the displacement amount of the shutter 10 while furthermore the rotary bodies 4, 8 are arranged in non-contacting state, torque control is scarcely subjected to the surface conditions of the rotary bodies 4, 8 or the ambient environmental conditions and thereby high accuracy can be sustained for a long term.